gitlab: Update software to gitlab 8.6

Update GitLab software to

    - gitlab-ce 8.6.9 + NXD patches

      nexedi/gitlab-ce!1

    - gitlab-shell to 2.6.12 + 1 patch to remove unneeded hooks.old in *.git

      nexedi/gitlab-shell!1

    - gitlab-workhorse 0.7.1 + NXD patches.

      nexedi/gitlab-workhorse!1

      ( download speedup patches were reworked because of upstream changes.
	Please see details in the above MR and in fixup commits )

This only updates software and begins SR update to 8.6 - for now gitlab
instance becomes non-working -- we'll pull in configuration files
updates and fixups in the following patches.